The art of magnetic recording has sawn the progress of enhancement of performance such as switching to digital form, reduction of size and prolongation of performance time. In general, the recent trend of magnetic recording media allowing the use of a magnetic tape such as audio tape and video tape housed wound on a reel in a cassette is the reduction of diameter of reel core with the reduction of size of cassette. On the other hand, the trend of tape itself is greater length. As a result, the ratio of the winding radius R of the magnetic tape wound on the reel to the radius r of the reel core (R/r) (hereinafter referred to as “winding radius ratio”) tends to rise.
The reel core radius and maximum winding radius of DVC and DVCPRO systems are set forth in Table 1 below.
TABLE 1MaximumReel corewinding radiusWinding radiusradius (r)(R)ratio (R/r)DV5.9 mm14 mm2.4minicassetteMiddle7.5 mm21 mm2.8cassetteLarge cassette9.5 mm32 mm3.225 NBPS (126minutes)Large cassette7.5 mm32 mm4.225 MBPS (184minutes)
DVCPRO large cassette 25 MBPS (184 minutes) reel has the largest winding radius ratio in reels which have been put to practical use to date.
Tape cassettes having a large winding radius ratio are subject to a great load on the wound tape, particularly at the portion close to the core, while put in vibration during transportation or the like. Thus, the magnetic tape can be subjected to stepping from the winding surface of the magnetic tape or undergo winding looseness.
The conventional technique for solving these problems comprises winding the magnetic tape on the reel with a tension to harden the winding of the tape on the reel, inhibiting the occurrence of the aforementioned defectives during transportation. However, when the tape reel having a tape wound on a reel with a high tension is stored at a high temperature and humidity over an extended period of time, the shape of the reel core is transferred to the tape, possibly causing dropout during recording/reproduction.
Further, the recent trend is for more magnetic tape to have a smaller thickness for prolonged performance time. The tape having a reduced thickness has a reduced mechanical strength and thus is more weak to high tension.
As mentioned above, the prolongation of performance time of magnetic tape and the reduction of size of magnetic tape cause a problem that the winding hardness of tape and the transportability and recording/reproduction performance of tape cannot be fairly balanced.